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<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Access Methods</dl></b></td>
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<p align=center><b>Error support</b></p>
<p>Berkeley DB offers programmatic support for displaying error return values.</p>
<p>The <a href="../../api_c/env_strerror.html">db_strerror</a> function returns a pointer to the error
message corresponding to any Berkeley DB error return, similar to the ANSI C
strerror function, but is able to handle both system error returns and
Berkeley DB specific return values.</p>
<p>For example:</p>
<blockquote><pre>int ret;
if ((ret = dbp-&gt;put(dbp, NULL, &key, &data, 0)) != 0) {
	fprintf(stderr, "put failed: %s\n", db_strerror(ret));
	return (1);
}</pre></blockquote>
<p>There are also two additional error methods, <a href="../../api_c/db_err.html">DB-&gt;err</a> and
<a href="../../api_c/db_err.html">DB-&gt;errx</a>.  These methods work like the ANSI C X3.159-1989 (ANSI C) printf
function, taking a printf-style format string and argument list, and
writing a message constructed from the format string and arguments.</p>
<p>The <a href="../../api_c/db_err.html">DB-&gt;err</a> method appends the standard error string to the
constructed message; the <a href="../../api_c/db_err.html">DB-&gt;errx</a> method does not.  These methods
provide simpler ways of displaying Berkeley DB error messages.  For example,
if your application tracks session IDs in a variable called session_id,
it can include that information in its error messages:</p>
<p>Error messages can additionally be configured to always include a prefix
(for example, the program name) using the <a href="../../api_c/db_set_errpfx.html">DB-&gt;set_errpfx</a> method.</p>
<blockquote><pre>#define DATABASE "access.db"
<p>
int ret;
<p>
(void)dbp-&gt;set_errpfx(dbp, program_name);
<p>
if ((ret = dbp-&gt;open(dbp,
    NULL, DATABASE, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
	dbp-&gt;err(dbp, ret, "%s", DATABASE);
	dbp-&gt;errx(dbp,
		"contact your system administrator: session ID was %d",
    		session_id);
	return (1);
}</pre></blockquote>
<p>For example, if the program were called my_app and the open call returned
an EACCESS system error, the error messages shown would appear as follows:</p>
<blockquote><pre>my_app: access.db: Permission denied.
my_app: contact your system administrator: session ID was 14</pre></blockquote>
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